Question: What is the meaning of the disciples having spoken in all tongues?

Answer [by ‘Abdu’l-Baha]: The disciples taught in the language of the Kingdom. That language (or tongue) is the equivalent of all languages, for the Word of the Kingdom is an expression of heavenly significances and heavenly mysteries. Whosoever attains it, to him the realities and mysteries of creation are clear. The heavenly significances are the comprehensive reality of all tongues. Therefore, the Holy Spirit having delivered to the disciples the tongue of the Kingdom, they become conversant with the tongues of all nations. With whomsoever among the nations and peoples of the world they conversed, they proved to be co-linguists. Moreover, the known and taught languages of the present exceed a thousand tongues in number. Had the disciples known the literal languages, they should have, at least, transcribed the Gospel in the tongue of some one of the nations, while as a matter of fact it was written only in the Hebraic and the Greek. The Gospel was not even written in the Roman tongue which was at that time an official language, since the government was in the hands of the Romans. As the disciples were not proficient in the Roman tongues they did not write the Gospel therein. (‘Abdu’l-Baha, excerpts from a table talk in Akka in 1907, notes taken by Corine True; ‘Notes Taken at Acca’, booklet published by Baha’i Publishing Society, Chicago 1907)